2 * linux/arch/i386/mm/fault.c
4 * Copyright (C) 1995 Linus Torvalds
7 #include <linux/signal.h>
8 #include <linux/sched.h>
9 #include <linux/kernel.h>
10 #include <linux/errno.h>
11 #include <linux/string.h>
12 #include <linux/types.h>
13 #include <linux/ptrace.h>
14 #include <linux/mman.h>
16 #include <linux/smp.h>
17 #include <linux/smp_lock.h>
18 #include <linux/interrupt.h>
19 #include <linux/init.h>
20 #include <linux/tty.h>
21 #include <linux/vt_kern.h> /* For unblank_screen() */
22 #include <linux/highmem.h>
23 #include <linux/module.h>
25 #include <asm/system.h>
26 #include <asm/uaccess.h>
27 #include <asm/hardirq.h>
30 extern void die(const char *,struct pt_regs *,long);
33 * Unlock any spinlocks which will prevent us from getting the
36 void bust_spinlocks(int yes)
38 int loglevel_save = console_loglevel;
49 * OK, the message is on the console. Now we call printk()
50 * without oops_in_progress set so that printk will give klogd
51 * a poke. Hold onto your hats...
53 console_loglevel = 15; /* NMI oopser may have shut the console up */
55 console_loglevel = loglevel_save;
59 * Return EIP plus the CS segment base. The segment limit is also
60 * adjusted, clamped to the kernel/user address space (whichever is
61 * appropriate), and returned in *eip_limit.
63 * The segment is checked, because it might have been changed by another
64 * task between the original faulting instruction and here.
66 * If CS is no longer a valid code segment, or if EIP is beyond the
67 * limit, or if it is a kernel address when CS is not a kernel segment,
68 * then the returned value will be greater than *eip_limit.
70 * This is slow, but is very rarely executed.
72 static inline unsigned long get_segment_eip(struct pt_regs *regs,
73 unsigned long *eip_limit)
75 unsigned long eip = regs->eip;
76 unsigned seg = regs->xcs & 0xffff;
77 u32 seg_ar, seg_limit, base, *desc;
79 /* The standard kernel/user address space limit. */
80 *eip_limit = (seg & 3) ? USER_DS.seg : KERNEL_DS.seg;
82 /* Unlikely, but must come before segment checks. */
83 if (unlikely((regs->eflags & VM_MASK) != 0))
84 return eip + (seg << 4);
86 /* By far the most common cases. */
87 if (likely(seg == __USER_CS || seg == __KERNEL_CS))
90 /* Check the segment exists, is within the current LDT/GDT size,
91 that kernel/user (ring 0..3) has the appropriate privilege,
92 that it's a code segment, and get the limit. */
93 __asm__ ("larl %3,%0; lsll %3,%1"
94 : "=&r" (seg_ar), "=r" (seg_limit) : "0" (0), "rm" (seg));
95 if ((~seg_ar & 0x9800) || eip > seg_limit) {
97 return 1; /* So that returned eip > *eip_limit. */
100 /* Get the GDT/LDT descriptor base.
101 When you look for races in this code remember that
102 LDT and other horrors are only used in user space. */
104 /* Must lock the LDT while reading it. */
105 down(¤t->mm->context.sem);
106 desc = current->mm->context.ldt;
107 desc = (void *)desc + (seg & ~7);
109 /* Must disable preemption while reading the GDT. */
110 desc = (u32 *)&cpu_gdt_table[get_cpu()];
111 desc = (void *)desc + (seg & ~7);
114 /* Decode the code segment base from the descriptor */
115 base = (desc[0] >> 16) |
116 ((desc[1] & 0xff) << 16) |
117 (desc[1] & 0xff000000);
120 up(¤t->mm->context.sem);
124 /* Adjust EIP and segment limit, and clamp at the kernel limit.
125 It's legitimate for segments to wrap at 0xffffffff. */
127 if (seg_limit < *eip_limit && seg_limit >= base)
128 *eip_limit = seg_limit;
133 * Sometimes AMD Athlon/Opteron CPUs report invalid exceptions on prefetch.
134 * Check that here and ignore it.
136 static int __is_prefetch(struct pt_regs *regs, unsigned long addr)
139 unsigned long instr = get_segment_eip (regs, &limit);
144 for (i = 0; scan_more && i < 15; i++) {
145 unsigned char opcode;
146 unsigned char instr_hi;
147 unsigned char instr_lo;
151 if (__get_user(opcode, (unsigned char *) instr))
154 instr_hi = opcode & 0xf0;
155 instr_lo = opcode & 0x0f;
161 /* Values 0x26,0x2E,0x36,0x3E are valid x86 prefixes. */
162 scan_more = ((instr_lo & 7) == 0x6);
166 /* 0x64 thru 0x67 are valid prefixes in all modes. */
167 scan_more = (instr_lo & 0xC) == 0x4;
170 /* 0xF0, 0xF2, and 0xF3 are valid prefixes */
171 scan_more = !instr_lo || (instr_lo>>1) == 1;
174 /* Prefetch instruction is 0x0F0D or 0x0F18 */
178 if (__get_user(opcode, (unsigned char *) instr))
180 prefetch = (instr_lo == 0xF) &&
181 (opcode == 0x0D || opcode == 0x18);
191 static inline int is_prefetch(struct pt_regs *regs, unsigned long addr,
192 unsigned long error_code)
194 if (unlikely(boot_cpu_data.x86_vendor == X86_VENDOR_AMD &&
195 boot_cpu_data.x86 >= 6)) {
196 /* Catch an obscure case of prefetch inside an NX page. */
197 if (nx_enabled && (error_code & 16))
199 return __is_prefetch(regs, addr);
204 asmlinkage void do_invalid_op(struct pt_regs *, unsigned long);
207 * This routine handles page faults. It determines the address,
208 * and the problem, and then passes it off to one of the appropriate
212 * bit 0 == 0 means no page found, 1 means protection fault
213 * bit 1 == 0 means read, 1 means write
214 * bit 2 == 0 means kernel, 1 means user-mode
216 asmlinkage void do_page_fault(struct pt_regs *regs, unsigned long error_code)
218 struct task_struct *tsk;
219 struct mm_struct *mm;
220 struct vm_area_struct * vma;
221 unsigned long address;
226 /* get the address */
227 __asm__("movl %%cr2,%0":"=r" (address));
229 /* It's safe to allow irq's after cr2 has been saved */
230 if (regs->eflags & (X86_EFLAGS_IF|VM_MASK))
235 info.si_code = SEGV_MAPERR;
238 * We fault-in kernel-space virtual memory on-demand. The
239 * 'reference' page table is init_mm.pgd.
241 * NOTE! We MUST NOT take any locks for this case. We may
242 * be in an interrupt or a critical region, and should
243 * only copy the information from the master page table,
246 * This verifies that the fault happens in kernel space
247 * (error_code & 4) == 0, and that the fault was not a
248 * protection error (error_code & 1) == 0.
250 if (unlikely(address >= TASK_SIZE)) {
251 if (!(error_code & 5))
254 * Don't take the mm semaphore here. If we fixup a prefetch
255 * fault we could otherwise deadlock.
257 goto bad_area_nosemaphore;
263 * If we're in an interrupt, have no user context or are running in an
264 * atomic region then we must not take the fault..
266 if (in_atomic() || !mm)
267 goto bad_area_nosemaphore;
269 /* When running in the kernel we expect faults to occur only to
270 * addresses in user space. All other faults represent errors in the
271 * kernel and should generate an OOPS. Unfortunatly, in the case of an
272 * erroneous fault occuring in a code path which already holds mmap_sem
273 * we will deadlock attempting to validate the fault against the
274 * address space. Luckily the kernel only validly references user
275 * space from well defined areas of code, which are listed in the
278 * As the vast majority of faults will be valid we will only perform
279 * the source reference check when there is a possibilty of a deadlock.
280 * Attempt to lock the address space, if we cannot we then validate the
281 * source. If this is invalid we can skip the address space check,
282 * thus avoiding the deadlock.
284 if (!down_read_trylock(&mm->mmap_sem)) {
285 if ((error_code & 4) == 0 &&
286 !search_exception_tables(regs->eip))
287 goto bad_area_nosemaphore;
288 down_read(&mm->mmap_sem);
291 vma = find_vma(mm, address);
294 if (vma->vm_start <= address)
296 if (!(vma->vm_flags & VM_GROWSDOWN))
298 if (error_code & 4) {
300 * accessing the stack below %esp is always a bug.
301 * The "+ 32" is there due to some instructions (like
302 * pusha) doing post-decrement on the stack and that
303 * doesn't show up until later..
305 if (address + 32 < regs->esp)
308 if (expand_stack(vma, address))
311 * Ok, we have a good vm_area for this memory access, so
315 info.si_code = SEGV_ACCERR;
317 switch (error_code & 3) {
318 default: /* 3: write, present */
319 #ifdef TEST_VERIFY_AREA
320 if (regs->cs == KERNEL_CS)
321 printk("WP fault at %08lx\n", regs->eip);
324 case 2: /* write, not present */
325 if (!(vma->vm_flags & VM_WRITE))
329 case 1: /* read, present */
331 case 0: /* read, not present */
332 if (!(vma->vm_flags & (VM_READ | VM_EXEC)))
338 * If for any reason at all we couldn't handle the fault,
339 * make sure we exit gracefully rather than endlessly redo
342 switch (handle_mm_fault(mm, vma, address, write)) {
349 case VM_FAULT_SIGBUS:
358 * Did it hit the DOS screen memory VA from vm86 mode?
360 if (regs->eflags & VM_MASK) {
361 unsigned long bit = (address - 0xA0000) >> PAGE_SHIFT;
363 tsk->thread.screen_bitmap |= 1 << bit;
365 up_read(&mm->mmap_sem);
369 * Something tried to access memory that isn't in our memory map..
370 * Fix it, but check if it's kernel or user first..
373 up_read(&mm->mmap_sem);
375 bad_area_nosemaphore:
376 /* User mode accesses just cause a SIGSEGV */
377 if (error_code & 4) {
379 * Valid to do another page fault here because this one came
382 if (is_prefetch(regs, address, error_code))
385 tsk->thread.cr2 = address;
386 /* Kernel addresses are always protection faults */
387 tsk->thread.error_code = error_code | (address >= TASK_SIZE);
388 tsk->thread.trap_no = 14;
389 info.si_signo = SIGSEGV;
391 /* info.si_code has been set above */
392 info.si_addr = (void __user *)address;
393 force_sig_info(SIGSEGV, &info, tsk);
397 #ifdef CONFIG_X86_F00F_BUG
399 * Pentium F0 0F C7 C8 bug workaround.
401 if (boot_cpu_data.f00f_bug) {
404 nr = (address - idt_descr.address) >> 3;
407 do_invalid_op(regs, 0);
414 /* Are we prepared to handle this kernel fault? */
415 if (fixup_exception(regs))
419 * Valid to do another page fault here, because if this fault
420 * had been triggered by is_prefetch fixup_exception would have
423 if (is_prefetch(regs, address, error_code))
427 * Oops. The kernel tried to access some bad page. We'll have to
428 * terminate things with extreme prejudice.
433 #ifdef CONFIG_X86_PAE
434 if (error_code & 16) {
435 pte_t *pte = lookup_address(address);
437 if (pte && pte_present(*pte) && !pte_exec_kernel(*pte))
438 printk(KERN_CRIT "kernel tried to execute NX-protected page - exploit attempt? (uid: %d)\n", current->uid);
441 if (address < PAGE_SIZE)
442 printk(KERN_ALERT "Unable to handle kernel NULL pointer dereference");
444 printk(KERN_ALERT "Unable to handle kernel paging request");
445 printk(" at virtual address %08lx\n",address);
446 printk(KERN_ALERT " printing eip:\n");
447 printk("%08lx\n", regs->eip);
448 asm("movl %%cr3,%0":"=r" (page));
449 page = ((unsigned long *) __va(page))[address >> 22];
450 printk(KERN_ALERT "*pde = %08lx\n", page);
452 * We must not directly access the pte in the highpte
453 * case, the page table might be allocated in highmem.
454 * And lets rather not kmap-atomic the pte, just in case
455 * it's allocated already.
457 #ifndef CONFIG_HIGHPTE
460 address &= 0x003ff000;
461 page = ((unsigned long *) __va(page))[address >> PAGE_SHIFT];
462 printk(KERN_ALERT "*pte = %08lx\n", page);
465 die("Oops", regs, error_code);
470 * We ran out of memory, or some other thing happened to us that made
471 * us unable to handle the page fault gracefully.
474 up_read(&mm->mmap_sem);
477 down_read(&mm->mmap_sem);
480 printk("VM: killing process %s\n", tsk->comm);
486 up_read(&mm->mmap_sem);
488 /* Kernel mode? Handle exceptions or die */
489 if (!(error_code & 4))
492 /* User space => ok to do another page fault */
493 if (is_prefetch(regs, address, error_code))
496 tsk->thread.cr2 = address;
497 tsk->thread.error_code = error_code;
498 tsk->thread.trap_no = 14;
499 info.si_signo = SIGBUS;
501 info.si_code = BUS_ADRERR;
502 info.si_addr = (void __user *)address;
503 force_sig_info(SIGBUS, &info, tsk);
509 * Synchronize this task's top level page-table
510 * with the 'reference' page table.
512 * Do _not_ use "tsk" here. We might be inside
513 * an interrupt in the middle of a task switch..
515 int index = pgd_index(address);
520 asm("movl %%cr3,%0":"=r" (pgd));
521 pgd = index + (pgd_t *)__va(pgd);
522 pgd_k = init_mm.pgd + index;
524 if (!pgd_present(*pgd_k))
528 * set_pgd(pgd, *pgd_k); here would be useless on PAE
529 * and redundant with the set_pmd() on non-PAE.
532 pmd = pmd_offset(pgd, address);
533 pmd_k = pmd_offset(pgd_k, address);
534 if (!pmd_present(*pmd_k))
536 set_pmd(pmd, *pmd_k);
538 pte_k = pte_offset_kernel(pmd_k, address);
539 if (!pte_present(*pte_k))